The invention presented herein relates to the composition of zirconium(Zr) alloy having superior corrosion resistance and high strength. In particular, this invention relates to the alloys with superior corrosion resistance and high strength for fuel claddings, spacer grids, and core structural components in light water reactor(LWR) and heavy water reactor (HWR).
Zircaloy has been developed in the early 1960s and has been widely used as fuel rod cladding and structural elements of nuclear reactor core. As the operating conditions of nuclear power plants tend to be at high burn-up, increased operating, Zircaloy-4 could not be utilized as fuel rod cladding.
U.S. Pat. No. 4,649,023 relates to the zirconium alloys, which comprise the following alloy composition, and the manufacturing process of the intermediate and final product thereof. niobium, in a range of 0.5 to 2.0 wt. %;
tin, up to 1.5 wt. %; PA1 a third alloying element, minimum 0.25 wt. %; and PA1 the balance being zirconium. The third alloying element is one of constituent such as iron, chromium, molybdenum, vanadium, copper and tungsten. PA1 niobium, in a range of 0.5 to 2.0 wt. %; PA1 tin , in a range of 0.7 to 1.5 wt. %; PA1 one element from iron, nickel, and chromium, 0.07 to 0.28 wt. % (optional); PA1 carbon, up to 220; and PA1 the balance being of zirconium. PA1 tin, in a range of 0.8 to 1.2 wt. %; PA1 niobium up to 0.6 wt. % (typically up to 0.3 wt. %); PA1 iron, in a range of 0.2 to 0.5 wt. % (typically 0.35 wt. %); PA1 chromium, in a range of 0.1 to 0.4 wt. % (typically 0.25 wt. %); PA1 silicon, in a range of 50 to 200 ppm (typically 100 ppm); PA1 oxygen, in a range of 900 to 1800 ppm (typically 1600 ppm); and PA1 the balance being of zirconium. PA1 tin, in a range of 0.2 to 0.9 wt. %; PA1 iron, in a range of 0.18 to 0.6 wt. %; PA1 chromium, in a range of 0.07 to 0.4 wt. %; PA1 niobium, in a range of 0.05 to 0.5 wt. %; PA1 tantalum, in a range of 0.01 to 0.2 wt. %; PA1 vanadium, in a range of 0.05 to 0.1 wt. %; PA1 molybdenum, in a range of 0.05 to 0.1 wt. %; and PA1 the balance being of zirconium. PA1 niobium, in a range of 0.5 to 1.5 wt. %; PA1 tin, in a range of 0.9 to 1.5 wt. %; PA1 iron, in a range of 0.3 to 0.6 wt. %; PA1 chromium, in a range of 0.005 to 0.2 wt. %; PA1 carbon, in a range of 0.005 to 0.04 wt. %; PA1 oxygen in a range of 0.005 to 0.15 wt. %; PA1 silicon in a range of 0.005 to 0.15 wt. %; and PA1 the balance being of zirconium.
This alloy is characterized to have the a microstructure with homogeneously dispersed fine precipitates of less than about 800 .ANG.. This was included to improve corrosion resistance in high temperature steam by controlling its microstructure.
The zirconium alloy with similar corrosion resistance to that in U.S. Pat. No. 4,649,023 is suggested in U.S. Pat. Nos. 5,112,573 and 5,230,758. This alloy includes niobium in a range of 0.5 to 2.0 wt. %, tin in a range of 0.7 to 1.5 wt. %, at least one element selected from the group consisting of iron, nickel and chromium in a range of 0.03 to 0.14 wt. %, and carbon up to 220 ppm, wherein the total amount of nickel and chromium is at least 0.12 wt. %. And, corrosion resistance is improved by chromium and nickel in a range of 0.03 to 0.08 wt. %, respectively.
U.S. Pat. No. 5,125,985 discloses the zirconium alloys, which comprise the following alloy composition:
This improved the corrosion resistance and the strength by controlling the distribution and distance of the precipitates by optimizing the heat treatment and working conditions.
U.S. Pat. No. 4,879,093 discloses the zirconium alloy by adding up to 0.6 wt. % of niobium or up to 0.1 wt. % of molybdenum in the Zircaloy. The amount of oxygen was in a range of 1000 to 1600 ppm, and the equivalent diameter of precipitates was in a range of 1200 to 1800 .ANG.. U.S. Pat. No. 5,080,861 developed the zirconium alloy with the retention of coherency of barrier oxide layer at the interface for minimizing the corrosion acceleration due to the precipitation of hydrogon compound at the interface between metal and oxide. This alloy includes up to 0.6 wt. % of niobium, tin in a range of 0.5 to 1.0 wt. %, one element selected from the group consisting of tellurium, antimony and silicon up to 0.2 wt. %, less than 70 ppm of nickel, less than 200 ppm of carbon in the Zircaloy. The amount of oxygen was in a range of 900 to 2000 ppm, and the equivalent diameter of the precipitates was 1200 to 1800 .ANG.. The addition of tellurium, antimony and silicon decreases the hydrogen uptake and the precipitatation rate and makes the coherency retained at the interface between metal and oxide layer under the circumstances of the extended and high burn-up fuel, which improves the corrosion resistance.
The improved zirconium alloy based on the above patent, U.S. Pat. No. 5,080,861 and U.S. Pat. No. 4,879,093 was additionally issued in U. S. Pat. No. 5,211,774. This alloy, which has a similar alloy composition to that in the above patent, has improved properties in ductility, creep strength and corrosion resistance under the neutron irradiation. It comprises an alloying composition as follows:
In this alloy, silicon decreases hydrogen uptake, and decreases the variation of corrosion resistance due to various working condition.
U.S. Pat. No. 5,244,514 also discloses the zirconium alloy including a smaller amount of tin as compared with the former existing Zircaloys, and has a low capture cross section of thermal neutrons, superior corrosion resistance, low hydrogen uptake, good workability and improved creep resistance. This alloy is composed of vanadium up to 1.0 wt. %, up to 1.0 wt. % of niobium, up to 0.2 wt. % of antimony and tellurium, up to 0.5 wt. % of tin, iron in a range of 0.2 to 0.5 wt. %, chromium in a range of 0.1 to 0.4 wt. %, silicon in a range of 50 to 200 ppm, up to 2200 ppm of oxygen, and the balance being of zirconium. The vanadium compound(ZrV.sub.2), which is the precipitate formed in this alloy provides good creep resistance, coarsening resistance, low neutron absorption, and stability in neutron flux and in high burn-up.
Alloys with improved corrosion resistance by adjusting the composition of the former existing Zircaloy-4 or adding niobium, tantalum, vanadium and molybdenum are in U.S. Pat. No. 4,963,323, 5,017,336, 5,196,163. Alloy in U.S. Pat. No. 4,963,323 adjusted the composition of the former existing Zircaloy-4. That is, the amount of tin was decreased and niobium was added as compensation, and the amount of nitrogen was controlled to less than 60 ppm in this alloy. Therefore, the alloy included tin in a range of 0.2 to 1.15 wt. %, iron in a range of 0.19 to 0.6 wt. % (typically 0.19 to 0.24 wt. %), chromium in a range of 0.07 to 0.4 wt. % (typically in a range of 0.07 to 0.13 wt. %), niobium in a range of 0.05 to 0.5 wt. %, and less than 60 ppm of nitrogen. U.S. Pat. No. 5,017,336 discloses the improved Zircaloy-4 with niobium, tantalum(Ta), vanadium, and molybdenum, and this alloy comprises an alloy composition as follows:
And U. S. Pat. No. 5,196,163 discloses the improved zirconium alloy which composition is equal to that of U.S. Pat. No. 4,963,323 except adding tantalum in a range of 0.01 to 0.2 wt. % further.
In U. S. Pat. No. 5,560,790, the distance between the precipitates, Zr(Nb, Fe).sub.2 and Zr(Fe, Cr, Nb)was limited to the range of 0.20 to 0.40 .mu.m, and the volume of the precipitate containing iron was limited to 60% of the total volume of precipitate for the improvement of corrosion resistance. This alloy comprises an alloy composition as follows:
As described above, the efforts to improve the corrosion resistance and the mechanical strength of alloy have been done. However, considering the circumstances of the extended and high burn-up fuel for the low cost, the use of Zircaloys as material for fuel rod cladding becomes limited due to enhanced corrosion and irradiation creep. Therefore, the development of an advanced zirconium alloy with high strength and corrosion resistance has been required.
We, the inventors of this invention, have investigated the enhancement of the corrosion resistance for the improvement of the creep in neutron flux and the corrosion acceleration of zirconium alloy which can be utilized as fuel rod claddings, spacer grids and structural components under the circumstances of the extended and high burn-up fuel. We first tested the effect of adding elements on the corrosion resistance, tensile and creep characteristics considering the effect of neutron flux, cost, workability, forming ability with base material, and determined the content of elements and the composition of alloys. Thereby we developed the zirconium alloys having higher corrosion resistance and strength than the former existing Zircaloy-4.